Mix together marshmallow cream, vanilla, peanut butter and syrup. Melt in microwave on High for 30 seconds. Stir and continue microwaving at 15 second intervals til it can be stirred smooth. Add cereal and stir until well-blended. Press into 8x8 pan coated with cooking spray. (I press it in by putting a small baggie over each hand and spraying the baggie with cooking spray - works like a champ!) Refrigerate until cool. If desired, drizzle with the Hershey's syrup. Cut into 16 squares.